I use trusted moderators that are assisted by a couple of the plugins mentioned above. There's nothing better than using human management to keep non-humans (or 'bad' humans) out of your forums.

If they are human, they eventually give-up trying and/or 'reveal themselves' resulting in a hard warning and/or a temporary ban. (usually ending in a permanent ban unless they somehow redeem themselves)

Anyway, If they aren't human, which is usually pretty obviuos from the start, they get banned.